Archive for October, 2012


I hate connectors

October 26, 2012

I’ve hinted about my personal project… I’m still not going to be specific about it but I will say that there are six pieces connected together via cables, fairly complicated cables.

I’ve been working with my single prototype, built by ordering parts from Sparkfun and laboriously put together, particularly given my soldering skills. It isn’t that I can’t solder, just that I don’t do it often so I tend to over-engineer my connections making each built circuit look like a tiny tank. Of solder.

Anyway, I need to move from one prototype for me to develop the idea to several prototypes to test the unit with actual users. I’d like to go to ten prototypes because that is what I’d ask for the firmware team if I was at a real company. You know, one with funding. Let’s just say the ten prototypes will be expensive and talk about funding another time.

What I want to discuss today is about connectors. By the title, you may already have clued in my feelings on said topic. But there is so much more to it than that. The only way to express the horror is to describe the whole process.

I started out with the number of wires I need to go to each piece of my system (five). For my prototype, I went to an electronics store and looked around for things about the right size. The resident helper-gnome sold me a wire crimper… Like some sort of medieval torture device a crimper puts a metal sleeve (terminal) on a wire so I can put it into the connector housing I’d chosen. Then I could attach my housing to the pins jutting out of the connector header on the board.

Got that? The housing is on the cable, the wires go in to it via crimped terminals. The board has a header that connects to the cables housing.

Crimping the wires requires a special tool. The usual cost for such a tool is between $400 and $2000 dollars. My head reels at what a scam that is.

The gnome helped me choose a $40 crimper tool that will work on most connectors of a certain size (0.1″ if you must know) and a certain wire gauge. Of course, I have to do three times more work than the expensive version but I’ve this is a labor of love. Right?

So I learned made cables with all this and it was difficult. By the end, I was near blind and my hands hurt.  Right now, I need to make a couple cables longer (which means remaking them entirely). I’ve been putting it off for two weeks.

The pain of that is nothing compared the pain of trying to choose the correct connector for going forward.

I know I want a smaller connector for the small build than the prototype. And I need a lot of interconnects so cheap headers would be nice. I plan to have someone else make these cables but I need to be able to build extras or repair broken ones, so the tools can’t be horrendously expensive. Someday, when we build in the thousands, I might be able to get rid of connectors altogether actually soldering wires on to boards with some (unknown and magical) strain relief.

So, if you go to Digikey and search for connectors, you get a giant list of inexplicable things. There is no quick parametric search yet where I can enter the number of wires and the spacing. Like looking up the spelling of a word in the dictionary, you really have to know what you want before you get there.

I went for Board to Board – Arrays, Edge Type, Mezzanine. It had lots of options. And I got completely lost in the options. An EE friend came over to let me watch over his shoulder as he found some connectors for me. We ended up with a housing that is half the size of my current one, has keying (can’t plug it in backwards) . At the bottom of that page, you can see it links to mating products. Sorting out which of those would meet my needs meant reading about each one, trying to figure out what it meant. The datasheet didn’t exactly have a choose-your-own-adventure guide to connectors, more a terse listing of numbers and part drawings that looked like they were drawn by Escher.

We chose a header and selected terminals to crimp on to the wires. A complete set. And the EE thought that it would all work with my $40 crimper, though it might a little fussy.

In a different adventure, another EE came over and looked at all this. He said it was all wrong. Well, not all wrong. Just not right. Sure, it did all match which was good (better than my first on-my-own attempt). But my crimper wasn’t going to work… not really. I’d go blind first.

He suggested a different style of connectors (IDC) which don’t require terminals. (I didn’t think that was an option because I need discrete wires and not a ribbon but that is a detail, and they do make discrete wire IDC, it is just harder to find. As though I needed that.)

However, that connector variety still requires expensive crimpers. Though they don’t properly crimp so much as push things into the right place. The one we found online was only $80 on ebay but since its retail was $11,000 (boggle!), I wonder. Also, after 30 minutes of us both digging into the specs of the tool and the specs of the connectors he’d identified and assorted random standards, we determined it wouldn’t work for the connectors he’d chosen. Or any in the right size range.

The goal now is to haunt ebay and craigslist to find a second-hand crimper of the right size and then select connectors that work with that crimper. If anybody has a matrix of which crimpers work with which connectors, do let me know?  Until then, I’ll be going cross-eyed trying to figure it out.



Embedded systems conference call for abstracts

October 13, 2012

About a year ago, I was getting ready to push the giant, red button that said GO for my Making Embedded Systems book. I thought that once I was done writing, it would be finished. Then I thought once the figures and tech reviews were done, the book would be ready to go.  Surely once we fixed all of my misplaced commas, it was done, right?

Not really. Then I started doing promotion. I did two webinars for O’Reilly. Those are a lot of work. I also looked around for other promotion to do: speaking at schools, talking to magazines about reviewing my book, being in the scary “out there” to meet people and market my book.

I also wanted to present at the embedded systems conference in the spring, I’d attended for many years but here was my opportunity to speak! By the time the GO button was pressed and I came up for air, I’d missed the conference deadlines. There was a slot for someone to talk about LEDs but what do I know about LEDs?

Turns out, enough to fake it. With the wonderful help from EE Rob Mitchell, I did a live demo on how to take some Christmas lights and make them run from an Arduino (similar to Deep Darc’s blog post). I showed how I could make lights to leave up all year as they changed colors based on day of the year. We went from boxed lights and uninstalled software to working things, showing the process of cutting wires and loading software. We even talked about productization paths, methods for getting from idea to market and how to look at costs.

We had more show than information but it was fun. And live demos are tricky things; the audience is there to see you succeed. But if you crash, burn, and light a fire on stage, well, that’s ok too.

Even though we were in the LED section of the conference, we got all-access badges which let us go to any session we wanted. And we got access to the break room. It doesn’t sound like much, but it was where all the other speakers hung out. And there was lunch, coffee, assorted snacks, tables, and chairs. At times, it felt like heaven.

One thing there wasn’t, though, was women. I think I saw two other women the whole time I hung out there. I was kind of disappointed not to meet any other embedded systems people who share my gender, if only because they’d be the only ones who’d really appreciate my light-up shoes project.

So, this year, I looked in early October for the call for abstracts. It appeared, they were all set. Eeek! How could I have missed it again?!? Ahh, no, it just hadn’t opened yet. I emailed the track chair for my LED session (feeling guilty as I never wrote her that article I’d promised). That led to me talking to one of the organizers, actually getting to pitch a few ideas that aren’t open yet, maybe getting to co-chair a track. Whee!

The call for abstracts is open now. Go on, submit an idea or two. I’m most excited about the case studies for debug and test and the one about getting to “Hello World” in under five minutes. (Hey! That is what I did last year!)

And if anyone wants to join a panel, loosely on sensors, well, drop me a line. I’m percolating on my own ideas but happy to listen if someone wants to chat about theirs.

Here is a prototype for a light-up animal.  Naw, this is a jelly fish from the Monterey Bay Aquarium. But if your idea for a talk is a quarter as cool as this jelly is, please submit it.